you become confident within yourself that you are a guide to the blind, a light to those who are in darkness
Other versions
King James Version
And art confident that thou thyself art a guide of the blind, a light of them which are in darkness,English Standard Version
and if you are sure that you yourself are a guide to the blind, a light to those who are in darkness,New International Version
if you are convinced that you are a guide for the blind, a light for those who are in the dark,